Carboxyl-containing isobutene copolymers

ABSTRACT

Carboxyl-containing isobutene copolymers are obtainable 
     a) by cationic polymerization of a mixture of from 1 to 99 mol % of isobutene and from 99 to 1 mol % of a 2-methylalk-1-ene at less than 20° C. in the presence of a halogen-containing Lewis acid and 
     b) subsequent grafting of the isobutene copolymer obtainable in this manner with an α,β-ethylenically unsaturated carboxylic acid or carboxylic acid derivative at above 100° C. and in the presence of a free radical initiator. 
     Such carboxyl-containing isobutene copolymers are particularly suitable as adhesive raw materials or as sealing compounds.

This is a divisional of application Ser. No. 08/300,185, filed Sep. 2,1994, now U.S. Pat. No. 5,473,022.

The present invention relates to carboxyl-containing isobutenecopolymers, obtainable

a) by cationic polymerization of a mixture of from 1 to 99 mol % ofisobutene and from 99 to 1 mol % of a 2-methylalk-1-ene of 5 to 8 carbonatoms at less than 20° C. in the presence of a halogen-containing Lewisacid and

b) subsequent grafting of the isobutene copolymer obtainable in thismanner with an α,β-ethylenically unsaturated carboxylic acid orcarboxylic acid derivative at above 100° C. and in the presence of afree radical initiator.

The present invention furthermore relates to a process for thepreparation of such carboxyl-containing isobutene copolymers and theirconversion to crosslinked isobutene copolymers. The present inventionalso relates to the use of such isobutene copolymers as adhesive rawmaterial and as a sealing compound.

Polyisobutenes are prepared by cationic polymerization at lowtemperatures and are suitable, inter alia, as raw materials foradhesives and as sealing compounds. Depending on the field of use, lowmolecular weight or high molecular weight polyisobutenes may be used(Ullmanns Encyklopadie der technischen Chemie, 4th edition, volume 19,pages 221-1980).

For certain applications, for example in sealing compounds, the bondingof the highly nonpolar polyisobutene chain to the generally polarsubstrates, which together with the polyisobutene form the sealingcompound, is insufficient. Moreover, the viscoelastic behavior of thepolyisobutene in sealing compounds frequently leads to deformations,some of which go substantially beyond the tolerable extent.

In the case of polyolefins, the bonding to polar substrates is generallyachieved by grafting them subsequently with carboxyl-containingmonomers. In the case of polyisobutene, however, this is not possiblesince the polyisobutene is not sufficiently reactive for such a reactionwith carboxyl-containing monomers. All that is known is that copolymeresof isobutene with 2-methylalk-1-enes can be prepared by copolymerizationby means of Ziegler catalysts (DE-A 20 14 394). However, the resultingisobutene copolymers are obtained as low molecular weight, viscous oilswhich, owing to their poor stability, cannot be used for manyapplications, for example as sealing compounds.

It is an object of the present invention to provide novel isobutenecopolymers which do not have the disadvantages described and, owing totheir high stability, are suitable for many applications.

We have found that this object is achieved by the novel isobutenecopolymers described above.

In the process leading to the novel carboxyl-containing isobutenecopolymers, a mixture of from 1 to 99 mol % of isobutene and from 99 to1 mol % of a 2-methylalk-1-ene is first subjected to cationicpolymerization. A mixture of from 50 to 98, in particular from 70 to 95,mol % of isobutene and from 50 to 2, in particular from 30 to 5, mol %of a 2-methylalk-1-ene is preferably used. The mol % used are to beunderstood as meaning that the sum of the amount of isobutene used andthe amount of 2-methylalk-1-ene used is always 100 mol %. Instead of a2-methylalk-1-ene, a plurality of different 2-methylalk-1-enes may alsobe used.

The 2-methylalk-1-enes used may be in particular 2-methyl-but-1-ene,2-methylpent-1-ene, 2-methylhex-1-ene or 2-methyl-hept-1-ene,2-methylpent-1-ene being preferably used.

The cationic polymerization of the mixture of isobutene and2-methylalk-1-ene is usually carried out at less than +20° C., inparticular less than 0° C. A preferred preparation process is BASFAktiengesellschaft's belt process, in which the mixture of isobutene andthe 2-methylalk-1-ene is subjected to cationic polymerization on acontinuously moving steel belt in a solvent, preferably ethylene, in thepresence of boron trifluoride (Ullmanns Encyklopadie der technischenChemie, 4th edition, volume 19, pages 220-1980). The cationicpolymerization of the mixture of isobutene and 2-methylalk-1-ene canalso be carried out in conventional reactors of plastics technology,continuously, semicontinuously or batchwise, preferably in solution, insuspension or by mass polymerization.

The cationic polymerization a) of the mixture of isobutene and one ormore 2-methylalk-1-enes is usually carried out in the presence of ahalogen-containing Lewis acid, such as BX₃, AlX₃, SnX₄, TiX₄, SbX₆ orFeX₃, where X may be fluorine, chlorine, bromine or iodine. Thehalogen-containing Lewis acids initiate the cationic polymerization.Particularly preferably used halogen-containing Lewis acids are thehalides of boron and of aluminum, preferably boron trifluoride, borontrichloride or aluminum trichloride. The halogen-containing Lewis acidsare used in amounts of from 0.01 to 1, in particular from 0.05 to 0.1%,by weight, based on the monomers. It may be advisable to introduce thehalogen-containing Lewis acids into the reaction mixture in the form ofa 0.1-5 percent strength by weight solution in an inert solvent, forexample in ethylene. The average polymerization times are usually from0.01 to 5, in particular from 0.5 to 2, minutes.

The rate of the cationic polymerization process a) may furthermore becontrolled by cocatalysts. Protic compounds, such as alcohols,carboxylic acids, etc., but preferably alcohols, are among thesubstances suitable for this purpose. Acceleration of the polymerizationgenerally results in an increase in the molecular weight and a reductionin the catalyst requirement. The chain length of the isobutenecopolymers can be influenced, particularly with regard to shortening,by, for example, the addition of olefins (eg. n-butene),halohydrocarbons, mercaptans and alkyl halides, it being possible forthe reaction time and the catalyst requirement to increase, so that suchregulators may simultaneously act as catalyst poisons.

By a suitable combination of both types of regulators, it is possible toprepare the novel isobutene copolymer having the desired molecularweight.

Depending on the subsequent intended use, solution viscosities (limitingviscosity number I₀) of the isobutene copolymers of from 50 to 2,000ml/g can be established. This corresponds to an average molecular weightMv (viscosity average) of from 50,000 to about 10,000,000.

The copolymers obtained in this manner contain from 1 to 99, preferablyfrom 50 to 98, in particular from 70 to 95, mol % of isobutene and from99 to 1, preferably from 50 to 2, in particular from 30 to 5, mol % ofone or more 2-methylalk-1-enes.

The copolymers are then converted into the novel carboxyl-containingisobutene copolymers by grafting b) with α,β-unsaturated carboxylicacids or carboxylic acid derivatives.

α,β-unsaturated carboxylic acids or carboxylic acid derivatives are usedas graft monomers in the process leading to the novel isobutenecopolymers. α,β-unsaturated carboxylic acids or carboxylic acidderivatives are to be understood as meaning both α,β-unsaturated mono-and dicarboxylic acids and the ester, anhydride or amide derivativesthereof. Maleic acid, fumaric acid, itaconic acid, acrylic acid,crotonic acid or the anhydrides thereof are among the substancespreferably used, maleic anhydride being particularly suitable.

The grafting b) of the isobutene copolymers is preferably carried out atabove 100° C., in particular at from 120° to 300° C., both in solution,for example as a 1-40 percent strength by weight solution in an apolarsolvent, and in the melt. Apparatus suitable for this purpose are, forexample, kneaders and extruders. The grafting b) is initiated by freeradical initiators.

The free radical initiators used are usually organic azo compounds ororganic peroxides, the latter preferably being used. Particularlypreferred organic peroxide compounds have a half-life of one minute atfrom 60° to200° C. Among these compounds, dicumyl peroxide, monocumyl(tert-butyl) peroxide, di-tert-butyl peroxide,2,5-dimethyl-2,5-di-tert-butylperoxyhexane and2,5-di-methyl-2,5-di-tert-butylperoxyhex-3-yne are particularlynoteworthy.

In a preferred embodiment of the process leading to the novelcopolymers, the isobutene copolymer is metered together with the monomerto be grafted and the free radical initiator into a reactor whichcontains an inert solvent, and grafting is carried out at from 150° to300° C. for from 0.5 to 30 minutes. The monomer to be grafted ispreferably added in the liquid state, said monomer being either heatedbeforehand or dissolved in an inert solvent. The monomer to be graftedmay also be added to the reactor after melting of the isobutenecopolymer. The free radical initiator is usually added either in theabsence of a solvent or as a solution in an inert hydrocarbon.

The grafted isobutene copolymers obtainable in this manner usuallycontain from 0.01 to 1.0% by weight of the monomer to be grafted, ie. ofthe α,β-unsaturated carboxylic acid or its carboxylic acid derivative.

If the grafting reaction is carried out in a solution, the novelcarboxyl-containing isobutene copolymers are isolated by precipitation.

In order to increase the yield, it may be advisable in the graftingreaction also to use small amounts of a vinylaromatic, for examplestyrene, in addition to a solvent.

The grafting reaction is preferably carried out in the presence of from0.01 to. 1, in particular from 0.1 to 0.5%, by weight of the monomer tobe grafted. The free radical initiator is usually added in amounts offrom 0.01 to 1, in particular from 0.1 to 0.5%, by weight. The statedweights are based on the isobutene copolymer.

The novel carboxyl-containing isobutene copolymer is particularlysuitable as an adhesive raw material.

It is also possible to react the novel, carboxyl-containing isobutenecopolymers with organic crosslinking agents. This gives crosslinkedisobutene copolymers which are likewise novel.

The crosslinking reaction is carried out in a conventional mixer,kneader or extruder at from 150° to 300° C., in particular from 180 to250° C., and during a residence time of the reaction mixture of from 0.1to 10, in particular from 0.5 to 5, minutes. The crosslinking agent maybe introduced either in pure form or in the form of a solution in aninert solvent, for example in tetrahydrofuran, toluene, hexane orheptane.

Suitable crosslinking agents are the substances usually used incrosslinking reactions, in particular polyfunctional primary orsecondary amines, amino alcohols, alcohols or epoxy-containingcompounds. Compounds which contain at least two carbon atoms, forexample ethylenediamine, diethylenetriamine, triethylenetetramine,diethanolamine, triethanolamine, dipropanolamine, tripropanolamine,ethyleneaminoethylamine, dimethylethylenediamine,diethylaminopropylamine, dimethylneopentanediamine, 1,8-octanediamine,4,7-dioxadecane-1,10-diamine, polytetrahydro-furan-αω-diamine,dimethyldipropylenetriamine, neopentanediamine, dimethylaminobutanol,dodecyldiamine, hexamethylenediamine, diethanolamine,N,N-diethylaminopropylamine, 1,4-bis[2,3-epoxypropoxy]benzene,bis[2,3-epoxypropyl]ether and 1,2-5,6-bisepoxyhexane are preferred.Particularly preferred crosslinking agents are polyfunctional amines orpolyfunctional isocyanates.

The organic crosslinking agent is usually added to the isobutenecopolymer in amounts of from 0.5 to 500, preferably from 1 to 300, mol%, based on the content of the grafted comonomer.

It is also possible to carry out grafting and crosslinking in a singlestep and in one mixing apparatus, which is considerably cheaper in termsof process engineering.

The crosslinked isobutene copolymers, which are likewise novel, aremechanically very stable materials and also possess, inter alia, hightensile strength and high elongation at break. They are particularlysuitable as adhesive raw materials and as sealing compounds.

EXAMPLES 1 TO 4 AND COMPARATIVE EXAMPLES A AND B Example 1

Preparation of an isobutene copolymer

A mixture of 90 g of liquid isobutene (93.1 mol %) and 10 g of2-methyl-pent-1-ene (6.9 mol %) was cooled to -104° C. by adding 350 gof liquid ethylene. Thereafter, first 0.1% by weight, based on thecomonomers, of boron trifluoride in the form of a 1% strength by weightsolution in ethylene and then 0.1 g of isobutanol were added to thissolution, with the result that the polymerization was initiated. After20 seconds, the cationic polymerization had ended and the unconvertedcomonomers and the ethylene were allowed to evaporate off. This gave acopolymer comprising 93.1 mol % of isobutene and 6.9 mol % of2-methyl-pent-1-ene and having a limiting viscosity number I₀ of 98ml/g, corresponding to a viscosity average Mv of 255,000.

Example 2

Grafting of the isobutene copolymer

9.5 g of the copolymer obtained from Example 1 and 0.5 g of maleicanhydride were dissolved in 90 g of isododecane at 170° C. 0.25 g of2,5-dimethyl-2,5-di-(tert-butylperoxy)-hexane was added to thissolution, and the reaction was allowed to continue for 1 hour at thistemperature. Cooling and precipitation in acetone gave acarboxyl-containing isobutene copolymer containing 0.16% by weight ofmaleic anhydride.

Comparative Example A

0.5 g of maleic anhydride was added to 9.5 g of isobutene homopolymerhaving a limiting viscosity number I₀ of 103 ml/g, corresponding to aviscosity average Mv of 350,000, this procedure being carried outsimilarly to Example 2. The precipitated polymer contained no chemicallybonded maleic anhydride.

Example 3

In a twin-screw extruder (ZSK-30 from Werner & Pfleiderer), 10 kg perhour of the isobutene copolymer obtained from Example 1 werecontinuously plasticated, ie. melted, and were reacted with 0.5% byweight of maleic anhydride at 200° C. In a devolatilization zonedownstream of the reaction zone of the extruder, the reaction mixturewas freed from unconverted maleic anhydride. A carboxyl-containingisobutene copolymer containing 0.19% by weight of maleic acid wasobtained.

Comparative Example B

The isobutene homopolymer of Comparative Example A was reacted with 0.5%by weight of maleic anhydride as described in Example 3. The dischargedpolymer contained no chemically bonded maleic anhydride.

Example 4

Crosslinking of the grafted isobutene copolymer

In a 2-paddle kneader from Brabender, 50 g of the grafted isobutenecopolymer obtained in Example 2 were first kneaded at room temperatureand then crosslinked. During the actual crosslinking, the crosslinkingagents stated in the table below were then added over a period of 5minutes, and crosslinking was effected in each case in the course of 10minutes. Thereafter, the crosslinked isobutene copolymer obtained wasdischarged and was pressed between two Teflon films (1 mm apart) todetermine the tensile strength and elongation at break according to DIN53,504 at 80° C. The viscoelastic behavior of the film samples wasassessed visually.

The table below shows that the crosslinked isobutene copolymers (samplesNo. B-F) have in particular a substantially higher elongation at breakand reduced viscoelastic behavior compared with the uncrosslinked,merely grafted isobutene copolymer (sample No. A).

                  TABLE                                                           ______________________________________                                                          Tensile   Elongation                                                                            Viscoelastic                                      Additive  strength  at break                                                                              behavior*                                 Sample No.                                                                            [% by wt.]                                                                              [N/mm.sup.2 ]                                                                           [%]     at RT                                     ______________________________________                                        A       --        ˜0  355     5                                         B       TEA 0.5   0.1       640     2                                         C       TEA 1.0   0.1       750     1                                         D       TEA 0.5   ˜0  868     4                                         E       PI 0.5    0.1       1,142   3                                         F       PI 2.0    0.1       1,311   3                                         ______________________________________                                         *Viscoelastic behavior at room temperature (RT):                              Viscoelastic behavior:                                                        1 = not viscoelastic                                                          5 = highly viscoelastic                                                       TEA = triethanolamine                                                         PI = polyisocyanate (Basonat ® FDS 3391, registered trademark of BASF                                                                              

We claim:
 1. A crosslinked isobutene copolymer, obtained by reacting acarboxyl-containing isobutene copolymer with an organic crosslinkingagent, said carboxyl-containing isobutene copolymer being obtained bya)the cationic polymerization of a mixture of from 1 to 99 mo. % ofisobutene and from 99 to 1 mol % of a 2-methylalk-1-ene of 5 to 8 carbonatoms at less than 20° C. in the presence of a halogen-containing Lewisacid and b) subsequent grafting of the isobutene copolymer obtained instep a) with an α,β-ethylenically unsaturated carboxylic acid or ester,anhydride or amide derivatives of α,β-ethylenically unsaturatedcarboxylic acid at above 100° C. and in the presence of a free radicalinitiator.
 2. A crosslinked isobutene copolymer as defined in claim 1,wherein polyfunctional amines or isocyanates are used as organiccrosslinking agents.
 3. A crosslinked isobutylene copolymer as definedin claim 1 wherein the reaction of the carboxyl-containing isobutenecopolymer with the organic crosslinking agent is carried out at from150° to 300° C.